The present invention relates to a device that converts coherent input light, such as light from a semiconductor laser diode, to output light differing in wavelength from the input light.
There is considerable interest in converting light from, for example, the red or infrared wavelengths emitted by semiconductor laser diodes to shorter visible wavelengths. One known method of effecting such a conversion is to input coherent light into a nonlinear optical crystal, which generates light with twice the frequency (half the wavelength) of the input light. This process is referred to as second-harmonic generation (SHG). If two different wavelengths are input, the nonlinear optical crystal may generate light with the sum or difference of the two input frequencies, a process known as sum-frequency generation (SFG) or difference-frequency generation (DFG). SHG, SFG, and DFG depend on the law of energy conservation and certain phase-matching conditions, as will be described below.